The present invention relates generally to polyimide substrates for use relating to flexible printed circuits, tape-automated bonding (TAB) tapes, metal interconnectors for integrated circuits and other similar-type electronics applications. More specifically, the polyimide substrates of the present invention have advantageous dimensional stability due, at least in part, to an interpenetrating polymer network morphology which inhibits large-scale phase separation.
U.S. Pat. No. 5,129,029 to Uemiya, et al. teaches polyimide compositions having a combination of a thermosetting polyimide and a thermoplastic polyimide.
The compositions and methods of the present invention are directed to a high modulus interpenetrating network polyimide film of at least two polyimide components. The interlocked polyimide components can be synthesized by polymerizing a first polyamic acid precursor material to a viscosity of less than 1000, 500, 400, 300, 250, 200, 150, 125, 100, 75, or 50 centipoise and then end-capping the first precursor material. The end capping agents used are either a carboxylic anhydride or a silylating agent.
A second polyamic acid precursor material can then be intermixed with the first precursor material. The end capping of the first material largely inhibits further polymerization and thereby allows preferential polymerization of the second polyamic acid in and around the first polymerized material, thereby forming the interpenetrating network. A second end capping can optionally be used to control the amount of polymerization of the second precursor material.
Useful dianhydrides for use in the present invention include tetravalent aromatic structures represented by 
where X is a divalent organic group selected from among xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, and xe2x80x94C(CF3)2xe2x80x94 and useful diamine are divalent aromatic structure represented by 
where Y is a divalent organic group selected from the group consisting of xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, and xe2x80x94C(CF3)2xe2x80x94.
When the second polyimide is polymerized in the presence of the first polymer, the two polymers will generally exhibit less phase separation relative to a simple melt blending of one another. Such interpenetrated polyimide compositions of the present invention are ideally suited as metal interconnect circuit board materials for flexible printed circuits, tape-automated bonding (TAB) tapes, metal interconnectors for integrated circuits and other similar-type electronics applications.